function drawParticle(particles, index)

% particles are x and y coords; index are their importances in descend
% sequence

if length(particles) ~= length(index)
    error length(particles) ~= length(index);
end

for ii = 1:length(particles)
   color = [1 1 1].*(ii/length(index))^2;
   plot(particles(index(ii), 1), particles(index(ii), 2), 'x', 'Color', color);

end